The Question Bank is synchronized across platforms, so if you log in with the same username the system will remember you whether you're on your laptop, desktop, tablet, or phone. Which is helpful because:
-The system won't show the same user the same problem twice
-You'll be able to access/review your stats and old practice sets from any platform
-The Question Bank is integrated with the Veritas Prep Practice Tests, so any problem you see in the Question Bank that might someday move into the practice tests will still be marked as "complete" by your username so you won't see repeat questions in the tests.
The only difference with the app is that it doesn't include the Integrated Reasoning problems from the Question Bank so you'd need to be on a laptop or desktop for those (since some of the tools like sorting tables aren't optimal for touchscreen and we'd rather people get used to that functionality on a true computer the way they'll see it on the test).